1. Technical Field
The present disclosure relates to wireless communication systems, and more particularly to a mobile communication device that includes an FM radio transceiver.
2. Background Information
Wireless communication devices originally provided only the capability of voice communication. Now wireless communication devices have evolved from being only mobile telephones to providing other communication, information and entertainment capabilities. In addition to photography, computing and gaming functions, a currently available mobile communication device might also include a Bluetooth transceiver to communicate with an earpiece, a portable MP3 player, a global positioning system (GPS) unit, or a WiFi transceiver to enable communication via a LAN as opposed to over a cellular network. As additional communication functions are added, additional frequency synthesizers are required to generate the signals used to transmit and receive signals at the frequencies used by the various functions. For example, a cell phone that operates on the wideband CDMA 2100 (WCDMA) standard transmits and receives at the frequencies 2110-2170 MHz. The GPS unit on the cell phone receives positioning signals at 1575 MHz. The WiFi transceiver on the cell phone transmits and receives at 2412-2484 MHz. And the Bluetooth transceiver communicates with the earpiece using the frequencies 2620-2690 MHz.
As additional communication functions are added, however, the frequency synthesizers begin to interfere with one another. Where the frequency synthesizers generate their signals using inductor-capacitor (LC) tanks, the signals generated by each additional synthesizer can interfere with the inductors of the existing synthesizers. Where the frequency synthesizers generate their signals using ring oscillators, a large amount of power must be used to reduce the large amounts of phase noise that ring oscillators are known to produce. Because of the power constraints of battery-powered mobile communication devices, ring oscillators are typically avoided in synthesizer designs where low noise is required.
Thus, a design for a frequency synthesizer is desired that meets the power constraints of a battery-powered mobile communication device but yet that reduces the interference with the inductors of the other frequency synthesizers located on the same mobile communication device.